The physical setting of this poem is the narrator's den. He describes this room only as a "chamber," but because it houses books and a bust of Athena, it seems to be a study of some kind (line 16). In terms of time, the setting is late December, a "bleak" month that is often symbolic of the end of life because it is, literally, the end of the year (7). Further, it is midnight, and a "dreary" one -- it is probably cold and windy and kind of creepy and bare outside (1). Midnight is also often used as a symbol of death because it is the end, or death, of day.
The poem's conflict seems to be one of the character vs. Nature variety. Although the raven could be viewed as an antagonist, I would argue that the raven doesn't really oppose the narrator in any way; he simply provides a catalyst for the narrator to begin to explore his feelings regarding death and what happens after it; this makes death the antagonist, and the raven is only a symbol of death. The narrator immediately identifies the bird with death, saying that the raven has come from the "'Night's Plutonian shore,'" and he hopes that the bird was a gift from the angels to distract him and help him forget his "memories of Lenore" (47, 82). Then, however, he fears that the bird is a "'thing of evil'" (85), and he wishes to know if there is some cure for his pain, for death. Next, he asks the raven if, "'within the distant Aidenn,'" his soul will ever meet with Lenore again in heaven (93). And though he believes that the bird will leave him as others "'have flown before,'" he eventually realizes that the bird is "never flitting" and will never leave (58, 103). He can never forget that death is coming for him now that he has had such a brush with mortality, when his lover died, and so the bird that represents death will never leave him. Thus, it is the narrator's own fears of death, his own as well as the permanence of his beloved's, that he must grapple with.